Electroplating processor with wafer heating or cooling

ABSTRACT

In electroplating a wafer, the front and/or back side of the wafer is heated or cooled during processing. The wafer may be in contact with a backing plate of an electroplating processor. The backing plate may be heated via electrical heaters, by radiant heaters, or via a heated liquid or gas. The backing plate may alternatively be cooled using electric coolers or cooled liquid or gas. The heated or cooled backing plate then heats or cools the back side of the wafer largely via conduction.

TECHNICAL FIELD

The field of the invention is plating substrates such as semiconductor material wafers.

BACKGROUND OF THE INVENTION

Microelectronic devices such as semiconductor devices are generally fabricated on and/or in substrates or wafers. In a typical fabrication process, one or more layers of metal or other conductive materials are formed on a wafer. A large number of variables can affect the quality, uniformity and other characteristics of the plated metal layer, which in turn influences the yield, or the amount of good micro-scale devices obtained from the wafer. These variables may include plating time, plating current profile, electrolyte quality and additives, wafer surface and wetting characteristics, and others. As the size of micro-scale devices continue to get smaller, improved electroplating processors and methods are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, the same element number indicates the same element in each of the views.

FIG. 1 is a perspective view of an electroplating processor.

FIG. 2 is a perspective view of the bowl of the processor shown in FIG. 1.

FIG. 3 is a section view of the head of the processor shown in FIG. 1.

FIG. 4 is an enlarged view showing details of FIG. 3.

FIG. 5 is a section view of the processor shown in FIG. 1.

FIG. 6 is a section view of the head of an alternative design.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIGS. 1-2, a processor 10 may have a head 12 supported on a head lifter 14. The lifter may lift and rotate the head into a face up position for loading and unloading a wafer into and out of the processor, and rotate the head into a face down position for processing in electrolyte in the bowl 16 of the processor. The processor shown in FIGS. 1-2 is an example of the types of processors that may be used. Similar low profile processors having reduced height, and operating without rotating the head, may also be used.

As shown in FIG. 3, the head 12 may include a rotor 24 supported on a shaft 22 and a bearing 34, with the rotor 24 rotated by a motor 20. A backing plate 30 may be joined to the shaft 22 via a shaft plate 32. A bellows 38 may be used to seal components in the head 12 from processing liquids used in the processor, and associated vapors, while allowing axial movement of the backing plate for loading and unloading a wafer 50 into the rotor 24. A contact ring 42 on the rotor 24 has a large number of contact fingers for making electrical contact with the wafer 50. A contact ring seal may optionally be used to seal the contact ring off from the electrolyte. Representative rotors are described in U.S. Pat. Nos. 6,527,926, 6,699,373, 6,911,127 and 7,118,658, incorporated herein by reference.

As shown in FIG. 4, one or more heaters 60 may be provided on or in the backing plate 30 to heat the back side of the wafer 50. The heaters 60 may be electric resistive heaters which heat the backside of the wafer primarily through conduction through the backing plate. The heaters 60 may be positioned above recesses in the backing plate, as shown in FIG. 4, or the recesses may be omitted with the back side of the wafer substantially in direct contact with a flat bottom surface of the backing plate. Electrical current may be provided to the heaters 60 via slip rings, or other techniques.

Alternatively, the backing plate or other components of the rotor may be heated using hysteresis and/or eddy current heating. In this case, the backing plate material may be selected to provide preferred heating characteristics, without use of individual discrete heating components. In an alternative design the heaters 60 may be replaced by coolers, for example thermoelectric coolers. In this design, the backing plate is cooled in turn cooling the wafer.

FIG. 6 shows an alternative design similar to FIG. 3 but using heating lamps 70, such as infrared lamps, supported on a non-rotating part of the head, such as the head frame 74. In this design, the lamps may irradiate and heat the backing plate 30, which in turn heats the back side of the wafer 50. The backing plate 30 in this design may optionally be made of a highly thermally conductive material, or a material largely transparent to the heating radiation from the lamps, to evenly distribute the heat.

Alternatively the backing plate 30 may have through openings to allow the lamps 70 to shine directly onto the back side of the wafer. In another design, the backing plate 30 may have built in windows adapted to allow the heating radiation to pass through. In another design, the back side of the wafer may be heated by supplying a heated liquid or gas to the backing plate 30, or onto the back side of the wafer 50, optionally via the shaft 22, with a back side seal sealing the heated liquid within the rotor. Chilled liquid or gas may also be used to cool the back side of the wafer.

In an example of use, the front side of the wafer is moved into contact with the bath of electrolyte in the bowl 16. Electrical current is supplied to one or anodes in the bowl 16. The wafer is electrically connected to a cathode via the contact ring 42. The current flows through the electrolyte causing metal ions to plate out on the front side of the wafer, creating a metal layer. The heaters 60, lamps 70 and/or heating liquid may be used to heat the back side of the wafer. Since certain chemical reactions increase with temperature, certain plating characteristics may be improved. Specifically, heating the back side of the wafer may allow for better control of the plating reaction kinetics and mass transfer of metal ions onto the wafer, without changing the electrolyte bath. The wafer may optionally be heated or cooled to a temperature different from the temperature of the bath. In some methods, a temperature gradient may be maintained in the wafer. Heating the wafer during plating may also improve the plated metal film grain structure.

Heating the wafer may improve metal ion diffusion for high aspect ratio features. Mass transfer within vias of high aspect ration features is often limited to diffusion as the dominant mechanism. By increasing the temperature within the via, mass transfer may be improved because diffusion is temperature dependent. By heating the back side of the wafer, the bottom of a trench, via or other feature may be raised to a temperature slightly higher than the front side surface temperature, because the bottom of the trench is closer to the heat source. The temperature can therefore be used to affect diffusion and reaction kinematics at the bottom of the feature.

Heating may improve plating in areas that are denser or more open, which have more seed layer exposed to plating, and less photoresist. If photoresist is more insulative, more heat may be channeled to the more open areas. The increased temperature may increase the layer thickness in a dense region, which may improve within die (WID) uniformity. Heating also reduces surface tension, which may improve wetting during dwell steps. Heating may also improve mixing of the bath solution with water from a pre-wet step, to improve plating uniformity.

In some applications, the amount of heating may be limited by the thermal budget of the front side of the wafer. The methods described may optionally be used in face-up or face-down plating. In face-up plating, warmer electrolyte rising from the bottom of a via may aid in mixing and diffusion. The methods described may be used in bumping, RDL (redistribution layer) as well as TSV (through silicon via) plating.

FIG. 5 shows an alternative design having heaters 80 positioned for heating the front or down facing side of the wafer. The heaters 80 may be radiant heaters at or near the surface of the electrolyte in the bowl. The heaters 80 may optionally be partially or fully recessed into the top surface of the electric field shaping element 18 in the bowl 16. Multiple heaters 80 may be circumferentially and/or radially spaced apart. Since the bowl 16 and the field shaping element 18 are fixed, the heaters 80 may be hardwired to the processor power supply. The front side heaters 80 may optionally be used in combination with the other heaters or coolers described above.

The term wafer as used here means a substrate or workpiece on which microelectronic, micro-mechanical, micro-electromechanical, and/or micro-optical devices are formed. The methods described here may also be performed using other types of processors different from the processors shown in FIGS. 1-6, including processors not using a rotor or a backing plate.

Thus, novel methods and apparatus have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention therefore should not be limited except by the following claims and their equivalents. 

1. A method for electroplating a wafer, comprising: moving a front side of a wafer into contact with an electrolyte; passing electric current through the electrolyte and through a conductive film on the wafer; and heating or cooling the wafer to a temperature different from the temperature of the electrolyte.
 2. The method of claim 1 comprising heating or cooling the back side of the wafer.
 3. The method of claim 2 further including placing the wafer into a processor having a backing plate with the back side of the wafer in contact with the backing plate, and heating or cooling the wafer by heating or cooling the backing plate.
 4. The method of claim 3 including heating the back side of the wafer by heating the backing plate via at least one electric resistive heater on or in the backing plate.
 5. The method of claim 2 further comprising heating or cooling the back side of the wafer by applying a fluid onto the back side of the wafer.
 6. The method of claim 5 with the fluid comprising a heated or cooled liquid or gas.
 7. The method of claim 2 comprising heating the back side of the wafer via at least one radiant heat source.
 8. The method of claim 7 comprising heating the back side of the wafer via direct impingement of radiant heat onto the back side of the wafer.
 9. The method of claim 7 comprising indirectly heating the back side of the wafer by heating a backing plate via the radiant heat source, with the backing plate conducting heat to the back side of the wafer.
 10. An electroplating apparatus comprising: a vessel holding an electrolyte; at least one anode in the vessel; a head having a rotor including a backing plate, with the head movable to position a wafer held in the rotor into the electrolyte; a contact ring on the rotor electrically connected to the wafer and to a cathode; and a thermal source in the head for heating or cooling a back side of the wafer.
 11. The apparatus of claim 10 with the thermal source on or in the backing plate.
 12. The apparatus of claim 10 with the thermal source comprising a supply of heated or cooled liquid or gas supplied onto the back side of the wafer.
 13. The apparatus of claim 10 with the thermal source comprising at least one electrical resistance heater on or in the backing plate.
 14. The apparatus of claim 10 with the thermal source comprising a radiant heat source.
 15. An electroplating apparatus comprising: a vessel holding an electrolyte; at least first anode in the vessel; a head having a rotor including a backing plate, with the head movable to position a wafer held in the rotor into the electrolyte; a contact ring on the rotor electrically connected to the wafer and to a cathode; and at least one heater in the vessel positioned to heat the wafer.
 16. The apparatus of claim 15 with a down-facing front side of the wafer facing the vessel, and with the at least one heater positioned to heat an up-facing back side of the wafer. 